This invention relates to a transducing device for transducing a physical quantity into an output electric signal. The physical quantity may be, for example, pressure of a fluid supplied to the device or an acceleration given to the device.
Conventional transducing devices are disclosed in U.S. Pat. No. 4,576,181 issued to Wallace et al and in U.S. patent application Ser. No. 517,882 filed May 2, 1990, now U.S. Pat. No. 5,086,777 by Toshiyasu Hishii for assignment to the present assignee. According to the Hishii patent application, a transducing device comprises a dielectric substrate having a substrate surface. A semiconductor physical quantity sensor is mounted on a center portion of the substrate surface and is for sensing fluid pressure which a fluid has and is higher than atmospheric pressure. The sensor produces a sensed signal representative of the pressure. A temperature compensating circuit and a pressure sensitivity calibrating circuit etc. are disposed on the substrate surface outwardly of the center portion and are connected to the sensor by bonding wires, respectively. The dielectric substrate has an introducing hole for introducing the fluid into the transducing device.
The sensor comprises a die defining a die hollow space having an open upper end and a die height which is measured from the substrate surface. A diaphragm is disposed along the upper end. A resistor is diffused into the diaphragm and has a piezoresistive effect to produce the sensed signal when the fluid is led to the diaphragm through the introducing hole. The sensed signal is transmitted to the temperature compensating circuit and the pressure sensitivity calibrating circuit through the bonding wires and temperature compensated pressure calibrated and is produced as the output electric signal.
A first end of the bonding wire is bonded to the sensor. A second end of the bonding wire is bonded to, for example, the temperature compensating circuit. The length is about three and a half times the die height long. When the die height is, for example, 0.45 mm, it is necessary that the length is about 1.58 mm long.
It is difficult to shorten the length of the bonding wire. Moreover, the second end of the bonding wire is bonded to the temperature compensating circuit which must be located far away from the die. The transducing device therefore becomes bulky. In the transducing device, the dielectric substrate is made essentially of Al.sub.2 O.sub.3 and has an Al.sub.2 O.sub.3 thermal expansion coefficient of about 7.times.10.sup.-6. The die is made essentially of silicon and has a silicon thermal expansion coefficient of about 3.5.times.10.sup.-6. In this manner, the substrate and the die have a difference in the thermal expansion coefficients to cause thermal strain to the diaphragm. As a result, it is impossible to accurately transduce a physical quantity into the output electric signal.